The IEEE 802.21 standard provides a uniform set of functionalities that help enable and enhance handovers across different link layer technologies. In particular, IEEE 802.21 defines a media independent handover (MIH) function (MIHF) which resides in communications entities of several wireless systems capable of supporting inter-system handover.
At a high level, the enhanced handover capability involves an upper layer MIH User which can communicate with an MIH Function, either locally or remotely, over a transport medium. The MIH Function, in turn, interacts with link-layer devices through the use of technology-specific primitives.
Of particular relevance is the capability of an MIH User to acquire measurement reports from an MIH Function and the capability of an MIH Function to acquire measurement reports from the link layer devices through the use of standardized MIH primitives.
These measurement reports can be either obtained either locally on a mobile terminal, or remotely through the use of MIH Protocol Messages. These measurement reports form a key part in the decision-making process for handovers.
While the current specification of 802.21 provides mechanisms to obtain such measurement reports, the mechanisms have deficiencies that deprive implementers from the use of key functionality and complete control of the measurement-reporting process.
According to the draft version of the IEEE 802.21 standards, the following primitives and corresponding protocol messages are used by the MIH User to acquire measurement reports from an MIH Function that may be collocated or be a remote peer. The MIH_Link_Get_Parameters Request/Response primitive unconditionally provides the value of a parameter being requested by the MIH User. The report of the parameter is made through the use of the response message. The MIH_Link_Configure Request/Response allows configuration of thresholds such that when these preset thresholds are crossed, the MIHF provides the requesting MIH User with indications through the use of MIH_Link_Parameters_Report Indication. The MIHF uses the MIH_Link_Parameters_Report Indication primitive, once certain preset thresholds are crossed, to provide an indication to the MIH User that had set the thresholds. The indication contains values for the parameter on which the thresholds have been set.
Similarly, the MIHF is also provided with primitives to acquire values for various parameters from the local link layer devices. The Link_Get_Parameters Request/Response primitive unconditionally provides the value of a parameter being requested by the MIH Function. The report of the parameter is made through the use of the response message. The Link_Configure_Thresholds Request/Response primitive allows configuration of thresholds such that when these preset thresholds are crossed, the link layer device provides the requesting MIH Function with indications through the use of Link_Parameters_Report Indication. The link layer device uses the Link_Parameters_Report Indication primitive, once certain preset thresholds are crossed, to provide an indication to the MIH Function that had set the thresholds. The indication contains values for the parameter on which the thresholds had been set.
Currently, these messages only allow one-time reports, which result in less flexibility and control of the measurement-reporting process. Periodic measurement reports are not possible through the functionalities currently provided by the IEEE 802.21 draft standard. The MIH User cannot configure a reporting period on the MIH Function (either local or remote peer). Similarly, the MIH Function cannot configure a reporting period on a link layer device using the primitives presently available in IEEE 802.21.
In addition, the current IEEE 802.21 draft specifications have some further deficiencies as follows. The first deficiency is that the MIH Function cannot clear reporting conditions previously configured on the link layer devices. Secondly, the MIH Function cannot disable measurement-reporting from link layer devices. A third deficiency is that the MIH User cannot clear reporting conditions previously configured on an MIH Function (local or remote). Finally, the MIH User cannot disable measurement-reporting from an MIH Function (local or remote).
It would be desirable to efficiently resolve these deficiencies through minimal impact on the current IEEE 802.21 standard draft specifications. It would also be desirable to incorporate a solution to the existing IEEE 802.21 messages and primitives.